VEGETATION CLASSIFICATION AND MAPPING AT GETTYSBURG NATIONAL MILITARY PARK AND EISENHOWER NATIONAL HISTORIC SITE

Technical Report NPS/NER/NRTR--2006/058

Stephanie J. Perles_¹, Gregory S. Podniesinski¹, William A. Millinor², and Lesley A. Sneddon³

¹ Pennsylvania Natural Heritage Program
Pennsylvania Science Office of The Nature Conservancy
208 Airport Drive
Middletown, PA 17057

² Center for Earth Observation
North Carolina State University
5112 Jordan Hall, Box 7106
Raleigh, NC 27695

³ NatureServe
11 Avenue de Lafayette, 5th Floor
Boston, MA 02111

September 2006

U.S. Department of the Interior
National Park Service
Northeast Region
Philadelphia, Pennsylvania

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Executive Summary

Vegetation classification and mapping was conducted at Gettysburg National Military Park and Eisenhower National Historic Site, creating a current digital geospatial vegetation database for the parks. Classification and mapping was completed jointly for these two parks because the parks are geographically contiguous and are managed by the same natural and cultural resource personnel. Fifteen vegetation associations, Chestnut Oak Forest, Dry Oak – Mixed Hardwood Forest, Tuliptree Forest, Modified Successional Forest, Conifer Plantation, Virginia Pine Successional Forest, Sycamore – Mixed Hardwood Floodplain Forest, Bottomland Mixed Hardwood Forest, Palustrine Shrub Thicket, Successional Old Field, Agricultural Field, Pasture, Orchard, Wet Meadow, and Reed Canary Grass Riverine Grassland, that occur within the parks were identified and described in detail. These vegetation types are strongly influenced by the varied environmental settings of the parks and the mandate to preserve the topographic, landscape, and cultural features as they were in 1863, such that visitors and historians can fully understand and appreciate the Battle of Gettysburg.

One of the most influential environmental factors on the parks’ vegetation is the Gettysburg Sill, the large diabase intrusion that supports the forested areas of the Gettysburg National Military Park. Dry Oak – Mixed Hardwood Forest is the most abundant forest association in the parks. It is the primary vegetation association in the forested diabase sill area, but also occurs in the historic woodlots scattered throughout Gettysburg National Military Park. Chestnut Oak Forest and Tuliptree Forest are two other, less common, forest associations that occur in the diabase sill area. The low areas surrounding drainages and creeks are another environmental setting in which forested areas persist in the parks. Sycamore – Mixed Hardwood Floodplain Forest and Bottomland Mixed Hardwood Forest are typical of these topographically low areas.

The Modified Successional Forest association encompasses fragmented, disturbed forest stands that are dominated by early successional, weedy tree species, invasive plants, and vines. A few areas of Conifer Plantation remain where coniferous trees were planted, primarily on privately held lands. Virginia Pine Successional Forest occurs in two locations in Gettysburg National Military Park in which Virginia pine (Pinus virginiana) has become established.

The ongoing management to maintain the historic and cultural landscape strongly influences vegetation within the park. Agricultural Field is the most common vegetation association in the parks, covering over 40% of the parks’ area. The rotation of grasses on the Agricultural Field areas, as well as the many Successional Old Field, inactive Pasture, Wet Meadow, and Reed Canary Grass Riverine Grassland areas, contributes to the abundance of grasslands in the parks. These large expanses of grasslands provide critical habitat for several species of birds and mammals, including bobolink (Dolichonyx oryzivorus), grasshopper sparrow (Ammodramus savannarum), eastern meadowlark (Sturnella magna), loggerhead shrike (Lanius ludovicianus), short-eared owl (Asio flammeus), upland sandpiper (Bartramia longicauda), northern harrier (Circus cyaneus), barn owl (Tyto alba), and least shrew (Cryptotis parva). The Wet Meadow and Successional Old Field associations also provide habitat for several rare plant species, including rigid sedge (Carex tetanica), bog rush (Juncus biflorus), whiteroot rush (Juncus brachycarpus), Buxbaum's sedge (Carex buxbaumii), low spearwort (Ranunculus pusillus), orange coneflower (Rudbeckia fulgida), hoary frostweed (Helianthemum bicknellii), Heller's rosette grass (Dichanthelium oligosanthes var. oligosanthes), eastern smooth beardtongue (Penstemon laevigatus), and sidebeak pencilflower (Stylosanthes biflora).

Invasive exotic plant species, such as multiflora rose (Rosa multiflora), Japanese barberry (Berberis thunbergii), tree of heaven (Ailanthus altissima), Asiatic tearthumb (Polygonum perfoliatum), Japanese stilt grass (Microstegium vimineum), Japanese honeysuckle (Lonicera japonica), Amur honeysuckle (Lonicera maackii), and Morrow’s honeysuckle (Lonicera morrowii), are an important threat to the native vegetation at Gettysburg National Military Park and Eisenhower National Historic Site. Chemical and mechanical control of these species should continue in order to protect the native vegetation associations.

A map showing the locations of vegetation associations in the parks was created following the USGS/NPS Vegetation Mapping Program protocols (The Nature Conservancy and Environmental Systems Research Institute 1994a, b, c). These vegetation associations were also crosswalked to the Terrestrial and Palustrine Plant Communities of Pennsylvania (Fike 1999) and to the National Vegetation Classification System in order to provide a regional and global context for the parks’ vegetation. A dichotomous field key was developed for these vegetation associations to assist with field recognition and classification.

This project documents the vegetation associations of Gettysburg National Military Park and Eisenhower National Historic Site based on 2003 aerial photography and 2004 field sampling, and completes one of 12 basic inventory data sets for the parks. However, battlefield rehabilitation in Gettysburg National Military Park has significantly altered the vegetation in many sections of the park; so much so, that the vegetation map was significantly out of date even before this report was published. Therefore, once the battlefield rehabilitation is completed, a new map of the vegetation associations should be completed based on the classification work presented in this report.

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Front matter through Project Area

pdf file 2
Materials and Methods

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Results through Modified Successional Forest

pdf file 4
Results--Conifer Plantation through Successional Old Field

pdf file 5
Results--Agricultural Field through Vegetation Map Production

pdf file 6
Discussion through to end